1. Field of the Invention
The present invention relates to an ink jet printing head for effecting printing by discharging a printing liquid (such as ink) as a flying liquid droplet and depositing such liquid droplet onto a printing medium, a manufacturing method therefor, and an ink jet printing apparatus.
The print herein includes that obtained by ink provision onto any ink receiving member capable of receiving such ink provision, including fabric, fiber, paper, sheet member etc., and the printing apparatus includes any information processing equipment or an output device thereof, and the present invention is applicable to these applications.
2. Related Background Art
In the field of the ink jet printing heads (hereinafter simply called printing heads) for effecting printing by discharging ink from a discharge opening, there is known a printing head utilizing an electrothermal transducer as the energy generating element for generating the energy required for ink discharge.
An example of such printing head is composed, as shown in FIGS. 1 and 2, of a substrate 2 (hereinafter also called heater board) provided thereon with a plurality of electrothermal transducers 1 as the energy generating elements, and a ceiling plate 6 which bears grooves 4 for forming ink paths 3 provided corresponding to the positions of the electrothermal transducers 1 and discharge openings 5.
The substrate 2 is provided thereon with a plurality of the electrothermal transducers 1 arranged in parallel manner at a predetermined pitch, and driving circuits (not shown) for driving the electrothermal transducers 1, which are formed by a semiconductor process including steps of etching, evaporation, sputtering etc., and is fixed to a support member 7. The substrate 2 is also provided, as shown in FIG. 2, with plural electrode pads 8 composed of aluminum and connected with the driving circuits of the electrothermal transducers 1. These electrode pads 8 are respectively connected, through aluminum or gold bonding wires 11, to wirings 10 of a circuit board 9 for receiving electrical signals from the recording apparatus (not shown).
On the other hand, the ceiling plate 6 is provided with a common liquid chamber 12 for temporarily holding the ink supplied from an ink tank (not shown), plural grooves 3 provided respectively corresponding to the positions of the electrothermal transducers 1 and communicating with the common liquid chamber 12, and discharge openings 5, opening on an end face of the ceiling plate 6 respectively from the ends of the grooves 3. The grooves 3 of the ceiling plate 6 constitute ink paths with the substrate 2, when the ceiling plate 6 is joined thereto.
The joining of the ceiling plate 6 with the substrate 2 is achieved in the following manner. At first the ceiling plate 6 is positioned with respect to the substrate 2 in such a manner that the electrothermal transducers 1 respectively correspond to the grooves 3, and is fixed for example with a plate spring (not shown). Then an adhesive material for temporary fixation is applied in the joining portions of the substrate 2 and the ceiling plate 6, thereby temporarily fixing the substrate 2 and the ceiling plate 6. Such adhesive material for temporary fixation is generally composed of a UV-curable polyester adhesive (for example UV300 supplied by Grace Japan Co., Ltd.). Finally, on the adhesive material for temporary fixation, there is coated resin of principally silicone family, thereby sealing the joining portions of the substrate 2 and the ceiling plate 6.
However, in the conventional ink jet printing head of such conventional configuration, since each ink path has a very small size, even a slight intrusion of the adhesive material or the sealing material causes clogging of the ink path. Such phenomenon causes insufficient or failed ink discharge in a part of the plural ink paths, thereby lowering the reliability of the ink jet printing head. For this reason, there has been desired a joining method without use of the adhesive material or the like, for the joining of the ceiling plate and the substrate in the manufacture of the ink jet printing head.
For meeting such requirement, there have been proposed methods as shown in FIGS. 3A-3C and FIGS. 4A-4E. These methods are to form the wall portion of the ink paths with a resinous material and to adjoin the substrate and the ceiling plate by the adhering force of the resinous material at the curing thereof.
FIGS. 3A-3C are cross-sectional views showing steps of a joining process by a DF (dry film) method.
In such DF method, at first a dry film 16 of a predetermined thickness is provided, as shown in FIG. 3A, on the upper surface of the substrate 2 for example by lamination. On the dry film 16, there are formed recesses for example by a photolithographic process utilizing a mask (not shown) of a predetermined pattern. The portions of the dry film 16, remaining on the substrate 2, constitute walls 17 of the ink paths as shown in FIG. 3B.
Then, as shown in FIG. 3C, the ceiling plate 6 is placed, via another dry film 18, on the substrate 2 bearing the ink path walls 17. The dry film 18 is thermally cured, and the ceiling plate 6 and the substrate 2 can be firmly joined by the adhesive force at the curing.
FIGS. 4A-4E are cross-sectional views showing steps of a joining process by a so-called molding method.
In the molding method, a resist layer 20 of a predetermined thickness is at first provided, as shown in FIG. 4A, on the upper surface of the substrate 2.
Then the resist layer 20 is subjected to a photolithographic process utilizing a mask (not shown) of a predetermined pattern, whereby portions corresponding to the ink paths remain as a mold 21 for the ink path formation.
Then, as shown in FIG. 4C, a resin layer 22 for forming the walls of the ink paths is formed on the substrate 2 and the mold 21.
Then the ceiling plate 6 is placed, via the resin layer 22, on the substrate 2. The resin layer 22 is thermally cured, and the ceiling plate 6 and the substrate 2 can be firmly joined by the adhesive force at the curing. Finally the face of the discharge openings is cut, and the resist constituting the mold is dissolved out for example with a solvent, thereby forming nozzles.
However, such DF method or molding method, though being capable of avoiding the clogging of the ink paths because of the absence of adhesive material, requires a patterning step in the joining, necessitating the use of an expensive exposure apparatus or the like.
For this reason, there has been desired a less expensive joining method.
For meeting such requirement, there is already known a joining method of mutually positioning the substrate bearing the energy generating elements and the ceiling plate provided with the ink paths and the discharge openings, and then fixing the ceiling plate and the substrate with a pressing spring.
FIG. 5 is an exploded perspective view of an ink jet unit including an ink jet printing head, for explaining the above-mentioned joining method for the ceiling plate and the substrate, utilizing the pressing spring.
In FIG. 5 there are shown a substrate 2 constituting a heater board, consisting of an array of plural electrothermal transducers (discharge heaters) 1 and electrical wirings such as of Al or the like for electric power supply thereto formed by a film forming process on a Si substrate, and a circuit board 9 for the heater board 2.
A grooved ceiling plate 6, provided with partitions (grooves) for separating the plural ink paths and a common liquid chamber for holding ink for supply to the ink paths, is integrally molded with an orifice plate 6a provided with plural discharge openings respectively corresponding to the ink paths. As a material for such integral molding there is preferably employed polysulfone resin, but other resinous materials for molding may also be utilized.
A support member 24, composed for example of a metal, supports the rear surface of the circuit board 9 in flat manner and constitutes the base plate of the ink jet unit. A pressing spring 25, constituting a pressing member, has an M-shaped form, and lightly presses the common liquid chamber by the central portion of the M-shaped form and also presses, in concentrated in linear areas, a part of the ink paths, preferably a part close to the discharge openings, by a hanging front portion 26. The legs of the pressing spring 25 pass through holes 24a, 24b of the support member 24 and engage with the rear face thereof to support the heater board 2 and the ceiling plate 6 therebetween in a mutually engaged state, and the heater board 2 and the ceiling plate 6 are pressed and fixed by the concentrated biasing force of the pressing spring 25 and the hanging front portion 26 thereof. An ink supply member 27 supplies the ink, fed from an unrepresented ink tank, to the ink paths of the heater board 2 through the ceiling plate 6 fixed thereto under pressure.
The above-explained joining method for the ceiling plate and the substrate by the pressing spring provides an advantage of easily achieving the aforementioned joining without the adhesive material, since the pressing is executed in a direction perpendicular to the surface of the substrate by means of the pressing spring.
It is however difficult, in such joining, to press the walls of the plural ink paths, formed between the ceiling plate and the substrate, against the substrate under a uniform pressure. For this reason, particularly in an ink jet printing head with a large number of the ink paths, there may result a gap C, as shown in FIG. 6, between the substrate 2 and an end portion of the ink path wall 3a, and such gap C results in a crosstalk phenomenon. Such crosstalk may lead to a pressure loss where the pressure of the film bubbling B, generated in the ink in the ink path 3 by the thermal energy from the heat generating member 1, leaks to an adjacent ink path (as indicated by the arrow in FIG. 6). Also because of the presence of such gap C, the pressure of the film bubbling B may propagate to the adjacent ink path, thereby inducing a retraction of the ink meniscus at the discharge opening (orifice) of such adjacent ink path toward the heat generating member and causing a fluctuation in the ink discharge amount.
In FIG. 6 there are also shown an anticavitation film 30, a protective film 31, and an interlayer insulation film 32.
The above-mentioned crosstalk is an extremely serious drawback in the ink jet printing head, and the prevention of such crosstalk is an important requirement.